Plastic components encompassing certain porosity are often created in response to the use of generative three-dimensional processes, such as the selective laser sintering or the three-dimensional print process, for example.
A thin layer of a powdery element is applied to a building platform in response to the selective laser sintering as well as in response to a three-dimensional print process. Subsequently, a part of the powder is selectively bonded, for example by means of applying binding material. This selection corresponds to a cut through the component, which is to be attained.
Subsequently, the building platform is lowered by a layer thickness and is provided with a new layer of particulate material, which is also solidified, as is described above. These steps are repeated until a certain desired height of the object has been reached. The imprinted and solidified areas thus create a three-dimensional object. Such a method is known from DE 69634921, for example.
Other powder-based rapid prototyping processes also operate in a similar manner, for example the electron beam sintering, whereby a loose particulate material is solidified selectively by means of a controlled, physical source of radiation.
All of these methods will be combined herein below under the term “generative three-dimensional processes”.
The components produced by means of generative three-dimensional processes oftentimes encompass certain porosity. For the most part, the porosity of the components is conditional on the method of the selective bonding. The connection by means of a laser beam corresponds to the sufficiently known sintering. The grains of the powder connect at their contact points by fusing together. The space between the grains remains open. The conditions of components, in the case of which the selective hardening is realized by metering a liquid (three-dimensional printing), are similar. A porous body is created in the event that the smallest possible quantity of liquid is metered as compared to the powder mass per unit of space. This is known from DE 60008778, for example.
Inadequate mechanical strength properties and disadvantageous surface characteristics are oftentimes problematic for the use of such porous components.
Similar to the known method for creating fiber reinforced materials, the absorptive capacity of porous parts makes it possible to introduce liquid media into the component.
It is thus known from DE 195 45 167 A1, for example, to cover a pattern, which is produced by means of selective laser sintering, with wax, so as to create a closed surface. Subsequent dipping processes in liquid shaped material require a liquid-tight part, so as to ensure the contour accuracy of the mold. What is important here are the strength characteristics. The method uses the thermal phase transition from solid to liquid and vice versa.
Disadvantageous the component must be subjected to considerable temperatures, depending on the infiltration material. In most cases, infiltration materials comprising a low melting point furthermore also encompass low mechanical properties.
In particular the characteristics of the used materials must be considered in response to the configuration of prototypes by means of the above-mentioned generative methods.
For example, it is known to use resins for the infiltration. The resins are introduced into the porous body in the form of a liquid and solidify in the component in the form of dispersion by evaporating the solvent or as resin mixtures by means of a polymerization. Such methods are known from WO 2005/82603 A1, from U.S. Pat. No. 6,375,874 and from U.S. Pat. No. 5,616,294, for example. Due to the necessity for the evaporation of the solvent, such dispersions described in these documents are only suitable for components comprising thin wall thicknesses. Due to the temperature sensitivity for porous plastic components, thermal methods following the example of wax infiltration are not very suitable to increase the strength.
For the most part, polymerizing mixtures for infiltrating are two-component systems, such as epoxy resins. Such mixtures attain high mechanical strength properties. However, they do not come close to the characteristics of commercially polymerized products, such as PE, PET, PMMA, etc., for example.
Polymerizing mixtures, as they are known from the state of the art, have the following limits.
The polymerizing infiltrate together with the porous component or also with the matrix, forms a composite material, which is weakened by the phase limits in the interior. The mechanical properties of the components thus always lie below values of the pure infiltrate.
Furthermore, one binding element and one resin element are typically mixed with one another prior to the introduction into the component in response to the use of a two-element system. The polymerization then begins in a time-delayed manner. It is a disadvantage of this method that once a mixture has been prepared, it must be processed within a short period of time. A dipping process, which provides for high quantities and for a high degree of automation, can thus not be realized in an economical manner. For the most part, the application is carried out by means of a brush. This method cannot be automated and requires high degree of effort in the case of complex geometries.